Transmission devices are gear trains that convert and transmit the power generated by a power source to comply with the load placed on the output shaft. Many prior art transmission devices, such as those commonly utilized in automobiles, require manual shifting among various gear ratios of the transmission. However, such transmissions are inherently inefficient due both to the loss of momentum caused by the removal of the power in order to change gears, and the inherent difficulty in determining the most efficient response to a load placed upon the output shaft.
A vast array of automatic transmissions are currently available. These transmissions do not require a manual determination of the most efficient response to a load placed upon the output shaft. In addition, they will typically reduce the time required to shift gears and, consequently, reduce the loss of momentum caused by the removal of power. Nonetheless, this loss of momentum, which is inherent in traditional automatic transmissions utilizing a variety of gear ratios, still results in a significant loss of power. In addition, the limited number of gear ratios available prevents these transmissions from achieving maximum efficiency.
In order to avoid momentum losses and attain maximum efficiency, it is desirable for a transmission to have a continuous, infinite range of gear ratios. Such a transmission would not require power to be removed in order to change gears and would be capable of efficiently responding to the various loads placed on the output shaft.
A number of United States Patents disclose continuous, or near-continuous, variable speed transmission. However, each has significant drawbacks. For example, U.S. Pat. No. 1,484,197 discloses a xe2x80x9cchange-speed transmissionxe2x80x9d that includes two conical wheels having teeth of uniform pitch throughout extending along the length of the cone and covering substantially one half of each conical surface. The cones are arranged to mesh with an intermediate wheel and are simultaneously rotated so that the teeth of one conical wheel move out of mesh with the intermediate wheel as the teeth of the other conical wheel move into mesh with the intermediate wheel. The gear ratio is varied by varying the position of the intermediate wheel relatively to the large and small diameters of the conical wheels.
This arrangement is successful at varying the gear ratio without loss of momentum. However, such a system creates inherently high shear stresses that severely limit its useful life. These shear stresses are explained by the fact that the circumference of the cylinder at its front and rear edges is the same, but these circumferences are forced to frictionally and rotatably engage with different-sized circumferences on the conical surface. As the wider portions of the conical surface travel faster than the narrower portions, the equal circumference of the cylinder respectively engages different-sized circumferences on the conical surface necessarily traveling at different speeds. This causes some portions of the cylinder to slip and rub against the faster conical portions resulting in shear forces.
U.S. Pat. Nos. 2,208,148 and 2,926,538 each describe a xe2x80x9cchange speed gearxe2x80x9d having a plurality of stepped gears arranged side by side on a cone drum and a cylindrical control gear displaceable disposed along a line of the surface of the cone of stepped gears on the driving shaft. Each stepped gear is diametrically subdivided and the two halves of the toothed rim of each step are displaced relative to each other. The spaces between steps are subdivided and staggered and the widths of the spaces is equal to half the width of the teeth of the control gear. The difference in the number of teeth from step to step is divided by two such that the opposite spaces between the points of bisection of the displaced rim halves of all steps are aligned. In operation, the control gear is caused to change its position relative to the cone drum in a synchronized manner such that it moves from one gear to the next in a stepped motion.
As this system utilizes the same cylindrical type control gear as described above, it suffers that same shear stress problems. In addition, the averaged tooth arrangement disclosed in these patents creates both wear and shock on the gears when changing from one set of teeth to another. For this reason, it is useful only at very low speeds.
U.S. Pat. No. 2,234,653 describes a variable transmission having two shafts around which series of teeth are wound. Each series of teeth forms a helix of decreasing diameter, with the teeth of one shaft being aligned with a space between teeth on the other. A spur gear is mounted between the shafts and is dimensioned to engage teeth on both shafts. The movement of the spur gear upward or downward causes it to engage teeth on both shafts, then teeth on only one shaft, and then teeth on both shafts again, with each movement causing an instantaneous change in the gear ratio.
This system does not require power to be removed from the transmission and provides the desired variability. However, the cylindrical nature of the spur gear of the compensation member causes it to suffer from the same shear stress problems described above. In addition, the use of substantially straight teeth causes discontinuous contact between teeth resulting in rapid increases and decreases in stress during gear changes.
U.S. Pat. No. 2,697,365, titled xe2x80x9cPower Transmission Equipmentxe2x80x9d, describes xe2x80x9ca mechanism for producing positive infinitely variable speed changes in a power transmission system.xe2x80x9d The mechanism includes xe2x80x9cat least two conical gear members having uniformly spaced teeth generated in a constant lead spiral path on the conical surface of each of said conical gear members.xe2x80x9d A compensation member, in the form of a spur gear, is interposed between, and engaged with, the conical members such that the axial position of the compensation member with respect to conical gear members determines the speed ratio obtained between the input and output members. In order to vary the speed ratio, the compensation member is disengaged from the conical members.
This system provides the desired variability. However, the cylindrical nature of the spur gear of the compensation member causes it to suffer from the same shear stress problems described above. In addition, the narrow tooth width required by this transmission decreases the overall strength of the teeth.
U.S. Pat. No. 2,875,628 describes a variable speed transmission that utilizes conical gears mounted in opposite relation to each other and each having sets of rigidly attached gear segments bounded by sets that are frictionally engaged with the rigidly attached segments. A spur gear is mounted between, and engaged with, the conical gears. The spur gear is adjustable upward and downward between the conical gears and shift gear ratios by moving from engagement with a rigidly attached gear segment to a frictionally engaged gear segment and then to the next rigidly attached gear segment.
This system is substantially continuous and provides an increased degree of variability. However, the cylindrical nature of the spur gear causes it to suffer from the same shear stress problems described above. Further, the lack of alignment between slopping and non-slipping teeth creates high stresses when going from a slipping portion to an adjacent non-slipping portion.
More recently, U.S. Pat. No. 5,407,399 describes a xe2x80x9cvariable speed friction transmissionxe2x80x9d as a variable ratio friction transmission in which a straight sided cone and a roller are in frictional engagement. The roller moves over an element of the cone to change the speed ratio, and at all times stays parallel to itself and moves along a straight line axis. This axis passes through the apex of the cone at all times, but the cone is tilted about its apex to contact the roller or wheel as the ratio is changed.
This system is substantially continuous and provides an increased degree of variability. In addition, the frictional engagement of the wheel with the cone eliminates the stress problems encountered with the meshing of spur gears with conical surfaces. However, the frictional engagement of this system severely limits it ability to operate under heavy loads. Further, frictional engagement is prone to wear and, consequently, the frictional surfaces on such a system would need to be replaced regularly.
U.S. Pat. No. 5,425,685 describes a xe2x80x9ccontinuously variable-ratio transmissionxe2x80x9d. This transmission includes a drive shaft having a series of curved teeth that are disposed in the same direction of the shaft and of such a shape that one end has a relatively small diameter and the other a relatively large diameter. A conical gear is engaged with the teeth and is flexibly attached to a splined shaft via a second gear and a universal joint. The splined shaft is attached to a second universal joint to allow it to maintain a constant angle relative to the surface of the shaft, allowing the conical gear to conform to the angle of the surface of the teeth formed on the shaft. In operation, the speed is changed by moving the conical gear up and back along the surface of the drive shaft.
This system is also substantially continuous and provides an increased degree of variability. However, it also relies upon frictional engagement, severely limiting its ability to operate under heavy loads and making it prone to wear.
U.S. Pat. No. 5,545,101 describes a xe2x80x9cfriction type continuously variable transmissionxe2x80x9d in which a planetary gear unit is attached to a frictionally engaged continuously variable unit. The planetary gear unit has a drive shaft, a carrier fixed to the drive shaft, a plurality of planetary gears supported on the carrier, and an internal gear meshing with the planetary gears. The continuously variable transmission unit has an input shaft to which is fixed to a sun gear meshing with the planetary gear.
This system is substantially continuous and provides an increased degree of variability. In addition, the frictional engagement of the wheel with the cone eliminates the stress problems encountered with the meshing of spur gears with conical surfaces. Finally, the integration of the planetary system allows the impeller to be rotated at a high speed even if the speed ratio of the continuously variable transmission unit is low. However, it is not without its drawbacks. As with all frictional systems, the frictional engagement of this system severely limits it ability to operate under heavy loads. Further, frictional engagement is prone to wear and, consequently, the frictional surfaces on such a system would need to be replaced regularly.
U.S. Pat. No. 5,601,509 describes a xe2x80x9ctaper roller continuously variable transmissionxe2x80x9d that includes a set of power input cones tapered in a first direction and a set of power output cones tapered in a opposite direction. Each cone has an axis of rotation oriented such that a portion of a surface parallel to a portion of the surface of each of the other cones in the same set. A power transfer ring tractionally engages the sets of cones on the parallel portions to transfer power from the input to the output set of cones. The power transfer ring is movable axially along the parallel portions to vary the speed ratio from the power input cones to the power output cones.
This system is also substantially continuous and provides an increased degree of variability. However, it again relies upon frictional engagement, severely limiting its ability to operate under heavy loads and making it prone to wear.
The present invention is a stack of gears, and transmission system utilizing the same, that overcomes the drawbacks of the prior art. In its most basic form, the stack of gears includes and a second gear disposed in parallel relation to, and sharing a common axis with, the first gear. Each gear is of a different diameter and each includes a plurality of teeth. At least one transition train is teeth disposed between the first gear and the second gear. Like the first and second gear, the transition train also includes a plurality of teeth that are disposed in substantially perpendicular relation to the common axis. The transition train is dimensioned to form at least one deceleration channel and at least one acceleration channel extending from each of the first gear and the second gear.
In some embodiments, the teeth of the stack of gears are dimensioned to mate with a pinion gear having an axis that is substantially parallel to the common axis of the first gear and the second gear. In some such embodiments a space between each of the third plurality of teeth of the transition train is substantially equal. In others, the teeth of the transition train forms an S-curve between the first gear and the second gear. Likewise, in others, the third plurality of teeth comprise teeth have a width equal to that of the teeth of the first gear and the second gear. In most embodiments, teeth may be straight teeth or helical teeth.
In some embodiments of the invention the stack of gears is dimensioned such that the acceleration channels and deceleration channels wrap around the stack several times by sharing teeth in the crossing channels. This differs from the VCT in that the VCT has to convert from a channel to a segment of a nascention circle, where the paths can cross, and then back to a channel.
It is preferred that the stack of gears also be able to be integrated into a control system used in connection with the transmission systems of the invention. In some such embodiments, the stack of gears includes at least a first conic surface disposed between the first gear and the transition train and a the second conic surface disposed between the transition train and the second gear. These conic surfaces preferably have a conic angle dimensioned to mate with a bumper of the pinion gear.
In some embodiments of the invention the stack of gears is dimensioned to mate with a continuous loop drive, such as a chain, a toothed belt, a V-belt, or a flat belt drive. In some such embodiments, the transition train of gears is angled to accept a twisted continuous loop drive. In others, two transition trains that cross each other over an intersection having substantially no teeth.
The basic embodiment of the transmission system includes the basic embodiment of the stack of gears, described above, and a mating member dimensioned to mate with the first plurality of teeth, the second plurality of teeth, and the third plurality of teeth of the stack of gears. As noted above, in some embodiments, this mating member is a pinion gear, while in others it is a continuous loop drive, such as a chain, a toothed belt, a V-belt, or a flat belt drive.
The preferred transmission system includes a control system for controlling the position of the mating member. In some embodiments utilizing a pinion gear, the control system includes at least a first conic surface and a second conic surface disposed upon the stack of such that the first conic surface is disposed between the first gear and the transition train and wherein the second conic surface is disposed between the transition train and the second gear. A pair of bumpers is disposed at an angle upon the pinion gear dimensioned to mate with a conic angle of the first and second conic surfaces. In some embodiments, the control system also includes a rail and a rocker arm slidably attached to the rail. The pinion gear is rotatably attached to the rocker arm and the rail is disposed in relation to the stack of gears such that the pinion gear is in contact with one of the first plurality of teeth, the second plurality of teeth, and the third plurality of teeth.
In some embodiments, the control system includes a resistance control for controlling a movement of the pinion gear. In one such embodiment, the control system includes a rail into which a track is disposed a shuttle slidably attached to the rail. The shuttle includes a bearing block disposed within and a pin that extends from the bearing block and fits within the track of the rail. The pinion gear is rotatably attached to the bearing block of the shuttle and the rail is disposed in relation to the stack of gears such that the pinion gear is in contact with one of the first plurality of teeth, the second plurality of teeth, and the third plurality of teeth. The subsequent movement of the gear is controlled by the resistance produced by the movement of the pin within the track.
The invention claimed herein has a number of similarities to, and a number of key differences from, the invention described and claimed in the inventor""s pending U.S. Pat. application Ser. No. 09/734,407, hereafter referred to as the xe2x80x9cVCTxe2x80x9d, of which this application is a continuation-in-part and, consequently, is herein incorporated by reference in its entirety.
As described in detail below, the present invention, hereafter referred to as the xe2x80x9cVCT2xe2x80x9d, is fundamentally different from the VCT in seven distinct ways. First, the axis of the pinion gear in the VCT2 is parallel with the axis of the cone, where the VCT had the gear axis parallel to the face of the cone. Second, the conix formula does not apply as the pinion gear can be a standard gear or any helical gear. Third, the VCT cone does not have to be a cone in the VCT2, as the angle between the ring gears can be constant, varied or curved. Fourth, the embodiment of the VCT described in FIG. 62 of the parent application will not work with the VCT2 , as the shaft the pinion gear is on is for controlling the position of the gear. Fifth, the VCT Felch cascade configuration will not work with the VCT2 because the cone cannot move independently and lateral movement of the inner and outer shaft would be unworkable. Sixth, the Persson configuration of the VCT2, described below, will not work with the VCT because the axes of all gears are parallel to each other. Seventh, as noted above, the channels of the VCT2 may cross by sharing teeth, while the channels in the VCT have to convert to a nascention ring segment where they cross and then start back into another channel.
The VCT2 is also similar to the VCT in many ways. For example, vector loading of the VCT applies directly to embodiments of the VCT2 where the first and second gears are helical gears, as these can still experience sideways pressure to move to a higher or lower gear range due to the vectoral force applied to the helical surface. In such an embodiment, the stack of gears of the VCT2 may have different helical teeth based on the environment. For example, a high torque environment would require a smaller helical angle then the lower torque, so that it did not move to easily.
Another similarity is in the designs of the acceleration and deceleration channels as the lateral motion in each should be an S-curve. Further, as with many embodiments of the VCT, embodiments of the VCT2 have an entrance, acceleration and deceleration tube and an exit. The speed in the entrance is the speed of the departing ring gear and the speed of the exit is the speed of the arriving ring gear. The tube is where the speed changes on a fractional basis making the change in speed continuous as opposed to stepped.
Yet another similarity is that both follow the same footprint analysis when laying out the movement of pinion gear through the channels is very similar, with both the VCT and VCT2 being adaptable for use with a variety of alignment and control surfaces.
Finally, as was the case with the VCT, the VCT2 may be utilized in a number of configurations. These may be grouped as cascading, planetary or differential.
Therefore, it is an aspect of the invention to provide a transmission that avoids momentum losses by not requiring power to be removed in order to change speed.
It is an aspect of the invention to provide a transmission that has an infinite range of gear ratios.
It is an aspect of the invention to provide a transmission that is capable of efficiently responding to the various loads placed on the output shaft.
It is an aspect of the invention to provide a transmission that avoids the shear stress problem attendant to the use of cylindrical spur gears in contact with conical gears.
It is an aspect of the invention to provide a transmission in which the arrangement of rings prevents excessive sliding within the gears.
These aspects of the invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, appended claims and accompanying drawings.